CONCORD, N.H. — Kathryn McDonough sat at the defense table — sometimes stoic and sometimes sobbing — as nearly a dozen members of Elizabeth “Lizzi” Marriott’s family berated her for betraying Marriott’s trust and luring the 19-year-old University of New Hampshire sophomore to her death.

McDonough, 19, had just pleaded guilty Thursday to hindering the prosecution, tampering with a witness and conspiracy for lying to investigators after Marriott’s family reported her missing last year. She had told investigators her new friend never showed up at the Dover apartment McDonough shared with 30-year-old Seth Mazzaglia as planned the night of Oct. 9.

McDonough was sentenced to 1½ to 3 years in prison and taken into custody at the end of the two-hour hearing.

Prosecutors say Marriott did arrive at the apartment that night and was killed by Mazzaglia, who is charged with first-degree murder.

The couple later admitted to investigators they used Marriott’s car to drive her body to Peirce Island in Portsmouth and threw it into the Piscataqua River, which feeds into the Atlantic Ocean. Her body has never been recovered, a fact her family lamented Thursday as intensifying their grief and robbing them of a chance to say goodbye.

Mazzaglia, who is being held without bond, is due in court Wednesday and his trial is scheduled to start in May. McDonough’s plea agreement calls for her to testify against Mazzaglia. Prosecutors have yet to say what transpired that night or what McDonough’s role was. She later admitted to investigators that she did nothing to render assistance to an unconscious Marriott or summon help.

Marriott family members said the charges McDonough pleaded guilty to don’t adequately convey her conduct or her culpability. They are classified as “victimless crimes” — a categorization Marriott’s mother disputed.

“Yours were the actions of a cold, calculating woman trying to stay out of trouble,” Melissa Marriott said. “Victimless? I don’t think so.”

Lizzi Marriott’s paternal grandmother, Susan Marriott, told McDonough, “You invited her to her death.” Her maternal grandmother, Charlotte Panneton, asked McDonough how she could live with herself.

“She gave you her friendship and you betrayed her,” Panneton said. “You did not stop the chain of events that took her life.”

Prosecutors say McDonough and Mazzaglia conspired and told investigators Mazzaglia accidentally strangled Marriott during consensual sex, an allegation Marriott family members said was reprehensible and deepened their pain. Prosecutors have been adamant there was nothing consensual about the circumstances surrounding Marriott’s death, but won’t elaborate.

McDonough’s lawyer, Andrew Cotrupi, said during the hearing that he wanted to dispel any notion that Marriott was somehow complicit in her death.

“Lizzi went to a friend’s house to watch a movie,” Cotrupi said. “She said no to a man that would not accept that. She is fully blameless in her death. Kathryn recognizes that.”

Just weeks before her death, Marriott began her first days as a transfer student at UNH, majoring in marine biology and commuting to campus from Chester, N.H., where she was living with relatives.

Bob Marriott, the victim’s father, said the family grudgingly accepted the plea deal to further the prosecution of Mazzaglia.

“I want to say goodbye to a person when they die,” he said. “That’s something I will never be able to do for my baby. I have gone to Peirce Island so many times and talked to the water. The defendant’s callous actions have caused me so much grief.”

Rockingham Superior Court Judge Marguerite Wageling, too, had harsh words for McDonough before officers cuffed her wrists behind her back and led her away.

“But for you, Elizabeth Marriott would be alive today,” Wageling said. “But for your cowardly and selfish actions, she would be alive or this family would have a body to lay to rest. You will carry that in your conscience the rest of your life.”